Have scriptSigFinalizer order sigs properly

Author: reardencode

test/integration/taproot.spec.ts

@@ -224,8 +224,8 @@ describe('bitcoinjs-lib (transaction with taproot)', () => {
     });
     psbt.addOutput({ value: sendAmount, address: address! });
 
-    psbt.signInput(0, leafKeys[1]);
     psbt.signInput(0, leafKeys[0]);
+    psbt.signInput(0, leafKeys[1]);
 
     const tapscriptFinalizer = buildTapscriptFinalizer(
       internalKey.publicKey,
@@ -344,9 +344,9 @@ describe('bitcoinjs-lib (transaction with taproot)', () => {
       leafPubkeys.push(toXOnly(leafKey.publicKey).toString('hex'));
     }
 
-    const leafScriptAsm = `${leafPubkeys[2]} OP_CHECKSIG ${
+    const leafScriptAsm = `${leafPubkeys[0]} OP_CHECKSIG ${
       leafPubkeys[1]
-    } OP_CHECKSIGADD ${leafPubkeys[0]} OP_CHECKSIGADD OP_3 OP_NUMEQUAL`;
+    } OP_CHECKSIGADD ${leafPubkeys[2]} OP_CHECKSIGADD OP_3 OP_NUMEQUAL`;
 
     const leafScript = bitcoin.script.fromASM(leafScriptAsm);
 

test/psbt.utils.ts

@@ -33,7 +33,20 @@ const buildTapscriptFinalizer = (
         redeem: { output: script },
         network,
       });
-      const sigs = (input.partialSig || []).map(ps => ps.signature) as Buffer[];
+      const stack = bitcoin.script.decompile(script);
+      if (!stack) throw new Error('Invalid script');
+      const pushes = stack.filter(chunk => Buffer.isBuffer(chunk)) as Buffer[];
+      const pkIdx = (pk: Buffer) => pushes.findIndex(chunk => pk.equals(chunk));
+      let sigs: Buffer[] = [];
+      if (input.partialSig) {
+        const pkIdxSigs = input.partialSig.map(ps => ({
+          idx: pkIdx(ps.pubkey),
+          sig: ps.signature,
+        }));
+        // Sigs need to be reverse script order
+        pkIdxSigs.sort((a, b) => b.idx - a.idx);
+        sigs = pkIdxSigs.map(({ sig }) => sig);
+      }
       const finalScriptWitness = sigs.concat(
         tapscriptSpend.witness as Buffer[],
       );